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United States Patent |
5,264,314
|
Mahabadi
,   et al.
|
November 23, 1993
|
Processes for the preparation of toners
Abstract
A process for the preparation of toner compositions which comprises mixing
at least one resin monomer with a polymerization initiator, a crosslinking
component and a chain transfer component; effecting bulk polymerization
until partial polymerization to near the onset of the gel-effect has been
accomplished thereby forming an organic phase containing a partially
polymerized component; mixing the aforementioned partially polymerized
component organic phase with pigment or dye particles; dispersing the
resulting organic phase in water containing a stabilizing component
whereby there is obtained a suspension of toner particles in water; and
polymerizing the toner suspension by heating.
Inventors:
|
Mahabadi; Hadi K. (Toronto, CA);
Cunningham; Michael (Georgetown, CA);
Wright; Heather (Burlington, CA);
Gardner; Sandra J. (Willowdale, CA)
|
Assignee:
|
Xerox Corporation (Stamford, CT)
|
Appl. No.:
|
858451 |
Filed:
|
March 27, 1992 |
Current U.S. Class: |
430/137.15 |
Intern'l Class: |
G03G 009/09 |
Field of Search: |
430/137
|
References Cited
U.S. Patent Documents
4077804 | Mar., 1978 | Vanzo | 430/137.
|
4601968 | Jul., 1986 | Hyosu | 430/137.
|
4626489 | Dec., 1986 | Hyosu | 430/137.
|
4816366 | Mar., 1989 | Hyosu et al. | 430/137.
|
4845007 | Jul., 1989 | Hyosu et al. | 430/137.
|
5043404 | Aug., 1991 | Mahabadi et al. | 526/194.
|
5164282 | Nov., 1992 | Mahabadi | 430/137.
|
Foreign Patent Documents |
41471 | Feb., 1991 | JP.
| |
Primary Examiner: Martin; Roland
Attorney, Agent or Firm: Pagazzo; E. O.
Claims
What is claimed is:
1. A process for the preparation of toner compositions consisting
essentially of mixing at least one resin monomer with a polymerization
initiator, a crosslinking component and a chain transfer component;
effecting bulk polymerization until partial polymerization to within from
1 to 5 percent of the onset of the gel-effect has been accomplished
thereby forming an organic phase containing a partially polymerized
component; mixing the aforementioned partially polymerized component
organic phase with pigment or dye particles; dispersing the resulting
organic phase in water containing a stabilizing component whereby there is
obtained a suspension of toner particles in water; and polymerizing the
toner suspension by heating.
2. A process for the preparation of color and black toner particles with
excellent pigment dispersion and which toner provides images with high
gloss and excellent projection efficiency which process comprises mixing
at least one resin monomer with a polymerization initiator, a crosslinking
component and a chain transfer component; effecting bulk polymerization
until partial polymerization to near the onset of the gel-effect has been
accomplished thereby forming an organic phase, where the degree of
conversion at which the gel-effect commences is related to the volume of
polymer, molecular weight of the polymer and the specific monomer/polymer
system wherein the conversion at the onset of the gel-effect x.sub.b is
represented by x.sub.b =K.sub.c d.sub.p /dM.sub.n.sup.0.5 where K.sub.c is
an entanglement parameter characteristic, d.sub.p is the density of the
polymer produced during polymerization, d is the overall density of the
monomer/polymer mixture and M.sub.n is the number average molecular weight
of the polymer formed during the bulk polymerization, mixing with the
aforementioned partially polymerized product pigment or dye particles;
dispersing the resulting organic phase containing said partially
polymerized product in water containing a stabilizing component whereby
there is obtained a suspension of toner particles in water; polymerizing
the toner suspension by heating and thereafter cooling enabling toner
particle with an average particle diameter of from about 3 to about 25
microns and with a narrow particle size distribution of about 1.1 to about
1.3; and wherein said bulk polymerization is accomplished up to conversion
of the comonomers to polymer within from about 1 to about 5 percent of the
conversion of the onset of said gel effect.
3. A process for the preparation of color and black toner particles which
comprises the bulk polymerization of comonomers with an
initiator/catalyst, a crosslinking component and a chain transfer
component up to a conversion of the comonomers within 1 to 5 percent of
the onset of the gel-effect where the onset of the gel-effect is defined
by x.sub.b =K.sub.c d.sub.p /dM.sub.n.sup.0.5 wherein x.sub.b is the onset
conversion for the gel-effect, Kc is a constant characteristic of the
monomer system, d.sub.p is the density of the polymer, d is the overall
density of the mixture and M.sub.n is the number average molecular weight
of the polymer generated during the bulk polymerization; terminating the
bulk polymerization by cooling the partially polymerized monomer; adding
colored pigments other than black, and optional additives to form the
organic phase, followed by mixing with a high shear mixer; dispersing the
organic phase into an aqueous phase containing an aqueous solution of
stabilizer and optionally an aqueous phase inhibitor with a high shear
homogenizer to enable a suspension with particles with an average particle
diameter of from about 3 to about 7 microns; heating to initiate
suspension polymerization, and retaining the mixture at a high temperature
of from about 50.degree. to about 120.degree. C. thereby completing the
conversion of comonomers to polymer; separating the polymer product by
filtration after cooling; and subsequently washing to eliminate the
stabilizer; followed by filtration and drying whereby there results toner
particles with an average particle diameter of from about 3 to about 10
microns and a narrow particle distribution of about 1.1 to about 1.3.
4. A process in accordance with claim 2 wherein from 1 to about 10 monomers
are selected.
5. A process in accordance with claim 2 wherein the dried toner particles
are blended with flow aid additives, and have incorporated therein charge
enhancing additives.
6. A process in accordance with claim 2 wherein the suspension of toner
particles in water is formed in a container and then transferred to a
reactor.
7. A process in accordance with claim 2 wherein the resulting toner
particles are of an average diameter of from about 3 to about 7 microns.
8. A process in accordance with claim 2 wherein the pigment particles are
cyan, magenta, yellow, red, blue, green, brown black, or mixtures thereof.
9. A process in accordance with claim 2 wherein bulk and suspension
polymerization is accomplished by heating to a temperature of from about
50.degree. to about 120.degree. C., the number and weight average
molecular weight of the polymer prepared in the bulk polymerization step
is from about 5,000 to about 50,000 and from about 10,000 to about
300,000, respectively, and the molecular weight distribution of the toner
polymer resin in the toner particles has one peak, or a plurality of
peaks.
10. A process in accordance with claim 2 wherein the dispersion of the
organic phase in the water containing stabilizing component is
accomplished with a high shear homogenizer.
11. A process in accordance with claim 2 wherein the particle size and
particle size distribution of the resulting toner is controlled by the
mixing time, stabilizing concentration, and the viscosity of the organic
phase during dispersion of the organic phase in the water containing
stabilizing component, and wherein the monomers are selected from vinyl
monomers.
12. A process in accordance with claim 2 wherein the monomers are styrene;
monocarboxylic acids and the derivatives thereof; dicarboxylic acids with
a double bond and the derivatives thereof; vinyl esters; vinyl ketones;
vinyl naphthalene; unsaturated mono-olefins; vinylidene halides; and
mixtures thereof.
13. A process in accordance with claim 2 wherein the monomers are styrene,
.alpha.-methylstyrene, p-chlorostyrene, acrylic acid, methyl acrylate,
ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl
acrylate, methacrylic acids, methyl methacrylate, ethyl methacrylate,
butyl methacrylate, octyl methacrylate, acrylonitrile or acrylamide;
maleic acid, monobutyl maleate, or dibutylmaleate; vinyl chloride, vinyl
acetate or vinyl benzoate; vinyl methyl ketone and vinyl ether ketone; and
vinyl ethyl ether or vinyl isobutyl ether; isobutylene; vinylidene
chloride; N-vinyl pyrrole; or mixtures thereof.
14. A process in accordance with claim 2 wherein the polymerization
initiator is selected from the group consisting of azo, diazo, peroxide
compounds, and mixtures thereof.
15. A process in accordance with claim 14 wherein the polymerization
initiator is azoisobutyronitrile, azodimethylvaleronitrile,
azobiscyclohexanitrile, 2-methylbutyronitrile, diazoamine-azobenzene,
dibenzoyl peroxide, di-(n-propyl) peroxydicarbonate, t-butyl benzoate,
t-amyl-(2-ethylhexyl) monoperoxydicarbonate, 2,2-di-(t-butylperoxy)
butane, dicumyl peroxide, t-butyl peroxide or mixtures thereof.
16. A process in accordance with claim 2 wherein the crosslinking component
is selected from the group consisting of ethylene glycol diacrylate,
ethylene glycol dimethylacrylate, divinyl ether, divinyl sulfite, divinyl
sulfone, divinylbenzene, and divinylnaphthalene.
17. A process in accordance with claim 2 wherein the chain transfer
component is selected from the group consisting of mercaptans and
halogenated hydrocarbons.
18. A process in accordance with claim 3 wherein the chain transfer agent
is carbon tetrachloride, butylmercaptan, or laurylmercaptan.
19. A process in accordance with claim 3 wherein the stabilizing component
is selected from the group consisting of nonionic and ionic water soluble
polymeric stabilizers, polyvinyl alcohol, gelatins, starches, gums,
alginates, zein and casein.
20. A process in accordance with claim 3 wherein the stabilizing component
is selected from the group consisting of methyl cellulose, ethyl
cellulose, hydroxypropyl cellulose, block copolymers, tricalcium
phosphate, talc and barium sulfate.
21. A process in accordance with claim 2 wherein the pigment is carbon
black, magnetites, nigrosine dye, Cl Solvent Blue 3
2,9-dimethyl-substituted quinacridone, an anthraquinone dye, a diazo dye,
Cl Solvent Red 10, Cl Pigment Red 48, or Cl Pigment Red 122.
22. A process in accordance with claim 2 wherein there is further included
as a component a charge enhancing additive selected from the group
consisting of alkyl pyridinium halide, a quaternary ammonium sulfate or a
quaternary ammonium sulfonate.
23. A process in accordance with claim 3 wherein there is further included
as a component a charge additive of stearyl phenethyl dimethyl ammonium
tosylate, distearyl dimethyl ammonium methyl sulfate, stearyl dimethyl
hydrogen ammonium tosylate cetyl pyridinium chlorides, or cetyl pyridinium
tetrafluoroborates; and wherein the resulting toner is blended with
surface additives.
24. A process in accordance with claim 3 wherein the polymer is methyl
methacrylate wherein K.sub.c ranges from 1.68 to 0.68 as the temperature
increases from 45.degree. C. to 90.degree. C., d.sub.p ranges from 1.19 to
1.16 over the temperature range of from about 45.degree. C. to 90.degree.
C., ranges from about 0.88 to about 1.19 and M.sub.n ranges from about
100,000 to about 150,000.
25. A process in accordance with claim 1 wherein the said bulk
polymerization is continued to within one percent of the onset of said gel
effect.
26. A process in accordance with claim 2 wherein the said bulk
polymerization is continued to within one percent of the onset of said gel
effect.
27. A process is accordance with claim 3 wherein the said bulk
polymerization is continued to within one percent of the onset of said gel
effect.
Description
BACKGROUND OF THE INVENTION
This invention is generally directed to processes for the preparation of
toner compositions, and more specifically, to semisuspension
polymerization processes for the preparation of black and colored, like
cyan, yellow, magenta, and the like, toners. In one embodiment, the
present invention is directed to semisuspension polymerization processes
for the economical preparation of toners with, for example, an average
volume diameter of from about 3 to about 25, and preferably from about 3
to about 7 microns, wherein a mixture of monomer or comonomers, a
polymerization initiator, a crosslinking component and a chain transfer
component are bulk polymerized until partial polymerization to the onset
of the gel-effect is accomplished; followed by adding to the formed
partially polymerized polymer pigments or dyes, optional additives such as
charge control materials, low molecular weight waxes, such as
polypropylene, or polyethylene, and the like to form an organic phase, and
then mixing this organic phase with, for example, a high shear mixer to
obtain a homogeneous organic mixture; subsequently dispersing the
resulting organic mixture in water containing a stabilizing component,
which dispersing can be accomplished, for example, by a high shear mixer;
transferring the resulting suspension to a reactor; and effecting
polymerization thereof; followed by cooling, optional washing, and drying.
The toner composition obtained can be optionally blended with surface
additives, which may function as flow aids, such as colloidal silicas and
the like. The gel-effect is a known phenomenon in the polymerization
process and the onset of the gel-effect can be indicated as a conversion
after which both the rate of polymerization and molecular weight of
polymer produced during polymerization increase rapidly. Conversion is
determined gravimetrically. The degree of conversion at which the
gel-effect commences is related to the volume of polymer, molecular weight
of polymer and the specific monomer system. This conversion x.sub.b can be
represented by x.sub.b =K.sub.c d.sub.p /dM.sub.n.sup.0.5 where K.sub.c is
an entanglement parameter characteristic of the particular system, d.sub.p
is the density of the pure polymer produced during polymerization, d is
the overall density of the monomer/polymer mixture and M.sub.n is the
number average molecular weight of polymer produced during polymerization.
Conversion at the onset of the gel-effect (x.sub.b) for a given
polymerization system can be calculated using this equation. In the
absence of a gel-effect, the conversion, x, at any time, t, during the
polymerization can be represented by x=1-exp(-kt) where x is the
fractional conversion of monomer to polymer, t is the reaction time and k
is a reaction rate constant. The onset of the gel-effect can also be
determined as that time of reaction at which the actual conversion exceeds
the conversion predicted by the equation x=1-exp(-kt) by a factor of 1.2,
that is the actual conversion exceeds the conversion that would be
obtained in the absence of gel-effect by 20 percent. In one embodiment,
the process of the present invention comprises the bulk polymerization of
comonomers, such as styrene methacrylates, like
styrene-n-butylmethacrylate or styrene acrylates, like styrene butyl
acrylate, and the like suitable for toner resins with an
initiator/catalyst up to a conversion of the comonomers to polymer which
is within from about 1 to about 5 percent of the conversion of the onset
of the gel effect; terminating the aforementioned bulk polymerization by
cooling the partially polymerized monomer or comonomers; adding pigments,
and other optional additives, such as charge additives followed by mixing
with, for example, a high shear mixer to form the organic phase;
dispersing this organic phase into the aqueous phase comprised of an
aqueous solution of a suspension stabilizer and optionally an aqueous
phase inhibitor such as potassium iodide; forming a suspension with, for
example, a high shear homogenizer with particles with an average volume
particle diameter of from about 3 to about 7 microns; heating to initiate
suspension polymerization, and retaining the mixture at a high temperature
of from about 50 to about (about as used herein includes points in between
the parameters recited) 120.degree. C. and more preferably from between
about 60 to about 80.degree. C., thereby completing the conversion of
comonomers to polymer, separating the polymer product by filtration after
cooling; and subsequently washing to eliminate the stabilizer; followed by
filtration, and drying, for example, by freeze drying, vacuum drying,
spray drying or fluid bed drying whereby there results polymer particles
with an average particle diameter of from about 3 to about 7 microns.
Advantages associated with the processes of the present invention in
embodiments include improved pigment dispersion, substantial avoidance of
coalescence, narrow particle size distribution, for example, from about
1.1 to 1.3, the preparation of small, for example in embodiments 3 to 7
microns diameter, black and color toners with high projection efficiency
and high gloss, and toner particles with less residual surfactant on the
surface and therefore better flow.
Toners have been prepared generally by fusion mixing of pigments
(colorants), charge control agents and other additives into thermoplastic
resins to disperse them uniformly therein. In view of the high viscosity
of the mixture, a considerable amount of energy is needed to achieve
uniform dispersion of pigments and other additives in the toner resin. The
mixture is then cooled, followed by pulverization and classification into
desired particle sizes and particle size distribution. It is known that
pulverization is an energy intensive step in this process. This
preparation method is capable of producing excellent toners, but requires
the use of several steps which are costly, energy intensive and are
limited in certain respects. In the process for producing toners by
pulverization, the material most usually be fragile so as to be readily
pulverized to a certain extent. Therefore, some thermoplastic resins which
are not fragile but have good fusing performance are not usually selected
for the aforementioned prior art processes. Also, if the material is too
fragile, it may be excessively micropulverized and, therefore, the fines
portion of the particles must be uneconomically removed. These limitations
become increasingly severe for smaller particle size toners. Moreover,
when a material with a low melting point is employed to improve fusing
performance of the toner, fusion of such material may occur in the
pulverizing device or the classifier.
Accordingly, in order to avoid or minimize the disadvantages of the
pulverization method, there have been proposed processes for producing
toner wherein the toner particles were formed and correct particle size
distribution produced in a reactor. These processes include dispersion
polymerization, suspension polymerization, emulsion polymerization, and
the like. Disclosed in U.S. Pat. No. 4,486,559 is the preparation of a
toner composition by the incorporation of a prepolymer into a
monomer/pigment mixture, followed by emulsion polymerization, see for
example columns 4, 5 and 8 of this patent. Also, methods of preparing
toner, including suspension/dispersion polymerization, are detailed in
columns 1 and 2 of this patent. In these processes, the pigment and
additives such as charge control components are added to a monomer or
comonomers prior to polymerization. Particle formation is achieved by the
dispersion of the pigmented monomer or comonomers in a continuous phase,
such as water, and the droplets of pigmented monomers are then polymerized
to form toner particles. One advantage of these processes as compared to
many other methods is the elimination of fusion mixing (Banbury/extruder)
and pulverization classification processing. Nevertheless, it can be
difficult with these processes to accomplish polymerization of pigmented
monomer droplets in a diameter range of 3 to 25 microns with a narrow
distribution of particle diameter of, for example, 1.3. Also, suspension
failure is common with these processes especially when monomer droplet
diameter is less than 50 microns and as polymerization proceeds in the
sticky region (10 to 60 percent conversion). Further, it is difficult to
conduct the polymerization of pigmented monomer droplets since, for
example, it is known that polymerization of free radical type monomers are
hindered, and many times prevented by the presence of various pigments,
especially carbon black. Another disadvantage of some of the prior art
processes for the preparation of toners resides in the resulting poor
dispersion of the pigment and other additives within particles which is
believed to be caused by the lack of mixing within individual particles
during polymerization and incompatibility of pigment with polymer produced
during polymerization which results in pigment aggregation. Moreover, some
of the prior art processes for the preparation of particles can be costly,
or not as economical as desired. These and other disadvantages are avoided
or minimized with the semisuspension polymerized toner processes of the
present invention.
Also mentioned are U.S. Pat. Nos. 4,486,559, which discloses the
incorporation of a prepolymer into a monomer toner mix followed by
emulsion polymerization; 4,680,200 and 4,702,988, which illustrate
emulsion polymerization; and 4,797,339 and 4,996,127 which disclose a
process in which small primary particles are produced by emulsion
polymerization, and then these particles are imbedded with pigment on the
surface and aggregated, thereby providing improved pigment dispersion,
however, this process involves many steps, thereby rendering it costly and
reducing yields. In addition, control of the molecular weight and
molecular weight distribution is difficult because of the very low
molecular weights required and the natural tendency of emulsion
polymerizations to produce very high molecular weights. Furthermore,
because the pigment is on the surface of the aggregated particle, charging
behavior of the toner can vary when different pigments are used.
In patentability search reports, there were recited as background U.S.
patents disclosing suspension polymerization U.S. Pat. Nos. 4,077,804;
4,601,968; 4,626,489; 4,816,366 and 4,845,007; 5,043,404 directed to
semisuspension polymerization; and 3,954,898, which discloses bulk and
suspension polymerization, see the Abstract for example.
In U.S. Pat. Nos. 5,164,282, the disclosure of which is totally
incorporated herein by reference, there are illustrated processes for the
preparation of toners, and more specifically, semisuspension polymerized
toner processes in which a mixture of monomer or comonomers, a
polymerization initiator, a crosslinking component and a chain transfer
component is bulk polymerized until partial polymerization, that is for
example from about 10 to about 40 percent of monomer or comonomers is
converted to a polymer; thereafter mixing the partially polymerized
product with pigments, optional charge control agents and other additives
with, for example, a high shear homogenizer to form a uniform organic
phase, dispersing the organic phase in water containing a stabilizing
component with, for example, a high shear mixer to produce a narrow
particle size toner suspension; and polymerizing the suspension product.
The toner obtained can then be washed/dried and dry blended with surface
flow aid additives. However, the processes described in U.S. Pat. No.
5,164,282 do not provide as good a dispersion as the process of the
present invention since, for example, it does not accomplish, for example,
the conversion at which the bulk polymerization must be terminated. In
U.S. Pat. No. 5,164,282, it is indicated that the bulk polymerization
should be conducted until partial conversion from 10 to 40 percent is
achieved, and this will not usually provide uniform dispersion of pigment
throughout the particle interior as individual pigment particles as
determined by transmission electron microscopy, but rather will result in
pigment particles migrating to the toner particle surface and/or
aggregating in clusters of primary pigment particles. In order to achieve
uniform dispersion of individual pigment particles throughout the particle
interior and control of micromixing, it has been found that the partial
polymerization should be conducted to within 1 to 5 percent of the onset
of the gel-effect, which depends on the temperature and molecular weight
of the polymer. Subsequently, when the suspension polymerization begins
after the organic phase is dispersed in the aqueous phase, the
polymerization rate, molecular weight and viscosity in the particle will
increase rapidly, thereby restricting diffusion of pigment and other
additives within the toner particles and ensuring good pigment dispersion.
Pigment dispersion is influenced primarily by the initial polymer
viscosity, which depends on the type of polymer, molecular weight of
polymer, polymer concentration and temperature, versus time profile in the
polymerizing particle and the size of the pigment particle. For a given
pigment diameter, pigment diffusion can be minimized by increasing the
initial viscosity of the organic phase and by reducing the time available
for diffusion to occur, which is the time between when the dispersion is
created and when the viscosity in the particles reaches a very high value,
typically when the conversion is greater than 80 percent, and by
maximizing the viscosity during that period initial viscosity of the
organic phase can be increased using semisuspension polymerization by
increasing polymer concentration and/or the molecular weight of the
polymer produced during the polymerization or by reducing the temperature.
Reducing the time available for diffusion to occur can be achieved by
conducting the suspension polymerization in the gel-effect regime so that
the rate of polymerization is very high, for example in the range of 0.05
to 1 moles/liter/minute. Therefore, these objectives can be achieved by
conducting the bulk polymerization to within 1 to 5 percent of the onset
of the gel-effect. When the bulk polymerization is terminated before the
onset of the gel-effect, the rate of viscosity increases and increasing
the conversion in the polymerizing toner particles will be more gradual
than when the bulk polymerization was terminated at the onset of the
gel-effect since the subsequent rate of increase of polymer concentration
will be less, and the viscosity is very sensitive to increases in
conversion (polymer concentration). This lower rate of increase in
viscosity will result in uncontrolled diffusion of pigment to the particle
surface and to the formation of clusters of primary pigment particles and
therefore overall poor pigment dispersion. If the bulk polymerization is
conducted beyond the onset of the gel-effect, the reaction will be very
difficult to control because of the rapid increase in the viscosity which
results in a wide GSD of the particles. Therefore, by terminating the bulk
polymerization within 1 to 5 percent of the onset of the gel-effect,
micromixing is controlled and pigment dispersion is improved, yielding
toner with high projection efficiency and high gloss in embodiments of the
present invention.
SUMMARY OF THE INVENTION
It is, therefore, an object of this invention to provide processes for the
preparation of toner compositions with many of the advantages illustrated
herein.
In another object of the present invention there are provided simple and
economical processes for the preparation of black and colored toners.
Another object of the present invention resides in simple and economical
processes for the preparation of black and colored toners with small size
particles and narrow particle size distribution with improved pigment
dispersion, permitting high projection efficiency of 7 to 100 percent and
high gloss, where a gloss level of less than 50 percent is considered low
and a gloss level of greater than 50 percent is considered high.
Further, another object of the present invention resides in simple
processes for the preparation of low cost, black and colored toners with
an average volume particle size diameter as determined by Coulter Counter
measurements of from about 3 to about 25, and preferably from about 3 to
about 7 microns, and narrow particle size distribution, preferably from
about 1.10 to about 1.35. The final particle size and particle size
distribution is affected by several factors; the initial particle size
distribution of the dispersion is affected by the organic phase viscosity,
the aqueous phase viscosity, type of stabilizer, concentration of
stabilizer, temperature, duration of shearing and type of dispersing
equipment used. The particle size distribution of the final toner product
is also affected by the above factors but it can be added to by
coalescence during the suspension polymerization. Coalesence occurs when
the conversion is low enough that particles are sticky and can adhere to
each other; coalesence ceases when the viscosity becomes sufficiently
high, typically when the conversion exceeds about 80 percent. Smaller
particles are more prone to coalesence and particle size distribution
broadening than larger particles, and therefore, for small particles it is
particularly important to minimize coalesence in order to minimize
broadening of the particle size distribution. By partially polymerizing
the monomers to within about 1 to 5 percent of the onset of the
gel-effect, the time available for particle coalesence is significantly
reduced and therefore particle size distribution broadening is minimized.
Additionally, in another object of the present invention there are provided
simple and economical processes for black and colored toner particles with
an average particle size diameter of 3 to 7 microns, a narrow particle
size distribution, a high degree of pigment and other additives
dispersion, that is for example the particles are dispersed as primary
particles and not aggregates and wherein these particles are uniformly
dispersed throughout the particle and are not all located at the particle
surface as measured by transmission electron microscopy, and a higher
degree of flexibility in controlling molecular weight and molecular weight
distribution of the toner resin without the use of
pulverization/classification can be accomplished. The combination of these
factors can also provide higher projection efficiency of transmitted light
as measured by the fraction of incident light that is transmitted through
a sample of the toner.
These and other objects of the present invention can be accomplished by the
provision of processes for the preparation of toners, and more
specifically, to semisuspension polymerized toner processes in which a
mixture of monomer or comonomers, a polymerization initiator, a
crosslinking agent and a chain transfer component is bulk polymerized
until to within about 1 to about 5 percent of the onset of the gel-effect;
thereafter mixing the partially polymerized product with pigments,
optional charge control agents and other additives with, for example, a
high shear homogenizer to form a uniform organic phase; dispersing the
organic phase into water containing a stabilizing component with, for
example, a high shear mixer to produce a narrow particle size toner
suspension and wherein the particles suspended possess, for example, an
average volume particle diameter of from about 3 to about 7 microns;
polymerizing the suspension product by heating, and thereafter cooling.
The toner obtained can then be washed/dried and dry blended with surface
flow aid additives to produce small size toner of from about 3 to about 7
microns with narrow particle size distribution of from about 1.1 to about
1.35 and with uniform distribution of primary pigment/additive particles,
and not clusters of primary particles in the interior of the toner
particle, and not concentrated primarily at the toner particle surface.
More specifically, the process of the present invention is comprised of (1)
mixing a monomer or comonomers with polymerization initiators, a
crosslinking component and a chain transfer component; (2) effecting bulk
polymerization by increasing the temperature of the mixture to from about
50.degree. C. to about 120.degree. C., and more preferably from 60.degree.
to 80.degree. C., until the degree of conversion is within 1 to about 5
percent of the onset of the gel-effect where the degree of conversion at
which the gel-effect commences is related to the volume of polymer,
molecular weight of polymer and the specific monomer/polymer system such
that the conversion at the onset of the gel-effect x.sub.b is given by
x.sub.b =K.sub.c d.sub.p /dM.sub.n.sup.0.5 where K.sub.c is an
entanglement parameter characteristic of the particular system, d.sub.p is
the density of the pure polymer produced during polymerization, d is the
overall density of the monomer/polymer mixture and M.sub.n is the number
average molecular weight of polymer produced during the polymerization;
(3) mixing with the aforesaid partially polymerized monomer product
pigments, charge control agents and other additive using a high shear
mixer to formulate a uniform organic phase; (4) dispersing the organic
phase into from 2 to about 5 times its volume of water containing from
about 1 to about 5 weight percent of a stabilizing component to form a
toner suspension with an average particle size of from about 5 to about 25
microns and a particle size distribution of from about 1.1 to about 1.3
using a high shear mixer; (5) transferring the resulting toner suspension
to a reactor and polymerizing by increasing the process temperature to
from about 55.degree. to about 120.degree. C. to complete the conversion
of monomer, or comonomers to polymer product; (6) washing the product with
water and/or an alcohol alkyl, 1 to about 20 carbon atoms, such as
methanol; (7) separating polymer particles by, for example, filtration or
centrifugation; (8) drying the toner particles obtained; and (9)
optionally dry blending with flow additives such as colloidal silica,
and/or charge control additives.
Also, the process of the present invention is directed to the preparation
of black and colored toner particles with an average volume particle
diameter of from about 5 microns to about 25 microns, and preferably about
3 to about 7 microns and with resin binders synthesized to have any
desirable average molecular weight, for example a number average molecular
weight of from about 5,000 to about 500,000, a weight average molecular
weight of from about 10,000 to about 2,000,000, and desired molecular
weight distribution, for example a molecular weight distribution with from
about 1 to about 4 peaks. Further, the process of the present invention is
directed to the preparation of black and colored toner particles of an
average diameter of from about 5 microns to about 25 microns, a particle
size distribution of from 1.1 to about 1.3 with the resin binder having a
number average molecular weight in the range of 5,000 to about 100,000,
and a weight average molecular weight of 25,000 to about 400,000; and a
molecular weight distribution having 1 to 3 peaks.
In one embodiment of the present invention, there is provided a process for
the preparation of toner particles which comprises mixing at least one
resin monomer with a polymerization initiator, a crosslinking component
and a chain transfer component; effecting bulk polymerization until
partial polymerization to within about 1 to about 5 percent of the onset
of the gel-effect is accomplished, where the degree of conversion at which
the gel-effect commences is related to the volume of polymer, molecular
weight of polymer and the specific monomer/polymer system such that the
conversion at the onset of the gel-effect x.sub.b is given by x.sub.b
=K.sub.c d.sub.p /dM.sub.n.sup.0.5 where K.sub.c is an entanglement
parameter characteristic of the particular system, d.sub.p is the density
of the pure polymer produced during polymerization, d is the overall
density of the monomer/polymer mixture and M.sub.n is the number average
molecular weight of polymer produced during polymerization; mixing with
the aforementioned partially polymerized monomer product pigment or dye
particles and charge enhancing component until a uniform organic phase is
formed; dispersing the organic phase in water containing a stabilizing
component whereby there is obtained a suspension of toner particles in
water; and polymerizing the toner suspension. Another embodiment of the
present invention is directed to a process for the preparation of toner
particles which comprises mixing resin monomer, comonomers, or mixtures
thereof with a polymerization initiator, a crosslinking component and a
chain transfer component; effecting bulk polymerization to within 1 to
about 5 percent of the onset of the gel-effect where the degree of
conversion at which the gel-effect commences is related to the volume of
polymer, molecular weight of polymer and the specific monomer/polymer
system such that the conversion at the onset of the gel-effect x.sub.b is
given by x.sub.b =K.sub.c d.sub.p /dM.sub.n.sup.0.5 where K.sub.c is an
entanglement parameter characteristic of the particular system, d.sub.p is
the density of the pure polymer produced during polymerization, d is the
overall density of the monomer/polymer mixture and M.sub.n is the number
average molecular weight of polymer produced during polymerization; mixing
with the partially polymerized monomer product pigments or dyes and charge
control materials until a uniform organic phase is formed; dispersing the
organic phase in water containing a stabilizing component thereby
obtaining a suspension of toner particles in water; polymerizing the toner
suspension wherein there is formed a toner product; and subsequently
washing and drying the toner particles.
The process of the present invention in another embodiment comprises (1)
mixing a monomer or comonomers with polymerization initiator with the
ratio of monomer or comonomers to initiator being from about 100/2 to
about 100/20, a crosslinking component with the ratio of monomer or
comonomers to catalyst component being from about 100/0.01 to about 100/5
and a chain transfer component with the ratio of monomer or comonomers to
the chain transfer component being from about 100/0.01 to about 100/1; (2)
effecting bulk polymerization by increasing the temperature of the mixture
to from about 50.degree. C. to about 120.degree. C. to a conversion of
within 1 to 5 percent of the onset of the gel-effect, as defined by the
aforementioned equation, to produce a polymer or polymers having a number
average molecular weight of from 5,000 to about 50,000 and a weight
average molecular weight of from about 10,000 to about 200,000; (3) mixing
with the partially polymerized monomer product from about 5 to about 70
weight percent pigment and one to 5 weight percent charge control agent
and other additives using a high shear mixer to form a uniform organic
phase; (4) dispersing the uniform organic phase to from about 2 to about 5
times its volume water containing from about 1 to about 5 weight percent
stabilizing component, preferably polyvinyl alcohol or hydroxypropyl
cellulose with a weight average molecular weight of from 1,000 to about
10,000 to form a toner suspension with a particle size of from about 5 to
about 25 microns with particle size distribution of from about 1.1 to
about 1.3 by using a high shear mixer; (5) transferring the resulting
toner suspension to a reactor and polymerizing the suspension by
increasing the temperature to from about 55.degree. C. to about
120.degree. C. to allow the complete conversion of monomer or comonomers
to polymer; (6) washing the product with equal volume of methanol and/or
water for 3 to 5 times; (7) separating toner particles from water/methanol
by means of filtration or centrifugation; (8) drying of the toner
particles; and (9) dry blending of toner with required additives such as
flow agent, and the like.
Illustrative examples of monomer or comonomers selected for the processes
of the present invention and present in effective amounts as illustrated
herein, for example, include vinyl monomers of styrene and its derivatives
such as styrene, .alpha.-methylstyrene, p-chlorostyrene and the like;
monocarboxylic acids and their derivatives such as acrylic acid, methyl
acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl
acrylate, phenyl acrylate, methacrylic acids, methyl methacrylate, ethyl
methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile and
acrylamide; dicarboxylic acids having a double bond and their derivatives
such as maleic acid, monobutyl maleate, dibutymaleate; vinyl esters such
as vinyl chloride, vinyl acetate and vinyl benzoate; vinyl ketones such as
vinyl methyl ketone and vinyl ether ketone; and vinyl ethyl ether and
vinyl isobutyl ether; vinyl naphthalene; unsaturated mono-olefins such as
isobutylene and the like; vinylidene halides such as vinylidene chloride
and the like; N-vinyl compounds such as N-vinyl pyrrole and the like; and
mixtures thereof. Generally styrene acrylates, styrene methacrylates,
styrene butadienes, and the like can be selected for the processes of the
present invention.
Examples of initiator present in effective amounts of from about 0.1 weight
percent to about 10 weight percent and more preferably from about 1
percent to 5 percent as illustrated herein, selected for the process of
the present invention, include azo and diazo compounds such as
azoisobutyronitrile, azodimethylvaleronitrile, azobiscyclohexanitrile,
2-methylbutyronitrile, diazoamine-azobenzene, mixtures thereof, and the
like and peroxide compounds such as dibenzoyl peroxide, di-(n-propyl)
peroxydicarbonate, t-butyl benzoate, t-amyl (2-ethylhexyl)
monoperoxydicarbonate, 2,2-di-(t-butylperoxy) butane, dicumyl peroxide,
t-butyl peroxide, and mixtures thereof. The bulk polymerization
temperature can be selected, for example, according to the initiator used.
Generally, the molecular weight of polymer decreases as the amount of
initiator or polymerization temperature increases. For example, the
molecular weight would decrease to from about 5,000 to about 25,000 as the
initiator concentration was increased from about 1.5 percent to about 6
percent. The bulk polymerization temperature, initiator types and
concentration should be selected to obtain monomer polymerized to within 1
to 5 percent of the onset of the gel-effect and to enable polymer with a
weight average molecular weight in the range of 10,000 to about 200,000.
This polymer will assist in the dispersion of pigment and also can coat
the pigment particle and, therefore, minimize the inhibition effects of
pigment on the suspension polymerization as well as further improving
pigment dispersion by reducing pigment aggregation.
The polymer in embodiments should preferably be crosslinked to some extent
to provide improved toner and/or image anti-offset characteristics.
Examples of crosslinkers selected for the process of the present invention
include compounds having two or more polymerizable double bonds. Specific
examples of such compounds include aromatic divinyl compounds such as
divinylbenzene and divinylnaphthalene; carboxylic acid esters with two
double bounds, such as aliphatic glycols like ethylene glycol diacrylate,
ethylene glycol; dimethylacrylate and the like; divinyl compounds such as
divinyl ether, divinyl sulfide, divinyl sulfone and the like. The
crosslinking component should preferably be present in an amount of from
about 0.1 to about 5 parts by weight in 100 parts by weight of monomer or
comonomers mixture.
Stabilizer present in effective amount of from about 0.01 percent to about
5 percent and more preferably from about 0.1 percent to about 2 percent as
illustrated herein, for example, and selected for the process of the
present invention includes nonionic and ionic water soluble polymeric
stabilizers such as methyl cellulose, ethyl cellulose, hydroxypropyl
cellulose, block copolymer, such as PLURONIC E87.TM. available from BASF,
the sodium salts of carboxyl methyl cellulose, polyacrylate acids and
their salts, polyvinyl alcohol, gelatins, starches, gums, alginates, zein,
casein and the like; and barrier stabilizers such as tricalcium phosphate,
talc, barium sulfate and the like.
The chain transfer component selected functions to control molecular weight
by inhibiting chain growth. Typical of chain transfer agents utilized for
the process of the present invention are mercaptans, such as
laurylmercaptan, butylmercaptan and the like, or halogenated carbons such
as carbon tetrachloride or carbon tetrabromide and the like. The chain
transfer agent should preferably be present in an amount of from about
0.01 to about 1 weight percent of monomer or comonomers mixture.
Numerous well known suitable pigments can be selected as the colorant for
the toner particles including, for example, carbon black, like Cl Pigment
Black 7, REGAL 330.RTM. carbon black, nigrosine dye, aniline blue,
phthalocyanine derivatives, magnetites and mixtures thereof. The pigment
should be present in a sufficient amount to render the toner composition
colored thereby permitting the formation of a clearly visible image.
Generally, the pigment particles are present in amounts of from about 3
percent by weight to about 20 percent by weight, based on the total weight
of the toner composition, however, lesser or greater amounts of pigment
particles can be selected.
When the pigment particles are comprised of magnetites or iron oxides,
including those commercially available as Cl Pigment Black 11, they are
present in the toner composition in an amount of from about 10 percent by
weight to about 70 percent by weight, and preferably in an amount of from
about 10 percent by weight to about 30 percent by weight. Alternatively,
there can be selected as pigment particles mixtures of carbon black or
equivalent pigments and magnetites, which mixtures, for example, contain
from about 6 percent to about 70 percent by weight of magnetite, and from
about 2 percent to about 15 percent by weight of carbon black.
Particularly preferred as pigments are magnetites as they enable, for
example, images with no toner spots for extended time periods exceeding
the development of 100,000 images, which corresponds to about 400,000
imaging cycles for a panel containing four imaging members.
Also embraced within the scope of the present invention in embodiments are
colored toner compositions containing as pigments or colorants red, blue,
green, brown, magenta, cyan, and/or yellow particles, as well as mixtures
thereof. More specifically, with regard to the generation of color images
utilizing the toner and developer compositions of the present invention,
illustrative examples of magenta materials that may be selected include,
for example, 2,9-dimethyl-substituted quinacridone and anthraquinone dye
identified in the Color Index as Cl 60710, Cl Dispersed Red 15, a diazo
dye identified in the Color Index as Cl 26050, Cl Solvent Red 10, Cl
Pigment Red 48, Cl Pigment Red 122, and the like. Illustrative examples of
cyan materials that may be used as pigments include copper tetra-4
(octadecyl sulfonamido) phthalocyanine, X-copper phthalocyanine pigment
listed in the Color Index as Cl 74160, Cl Pigment Blue, and Anthrathrene
Blue, identified in the Color Index as Cl 69810, Cl Pigment Blue 19, Cl
Solvent Blue 79, and the like; while illustrative examples of yellow
pigments that may be selected include diarylide yellow
3,3-dichlorobenzidene acetoacetanilides, a monazo pigment identified in
the Color Index as Cl 12700, Cl Solvent Yellow 16, a nitrophenyl amine
sulfonamide identified in the Color Index as Foron Yellow SE/GLN, Cl
Dispersed Yellow 33, 2,5-dimethoxy-4-sulfonanilide
phenylazo-4'-chloro-2,5-dimethoxy acetoacetanilide, Cl Pigment Yellow 31,
and the like. These pigments are generally present in the toner
composition in effective amounts, such as for example in an amount of from
about 2 weight percent to about 15 weight percent, based on the weight of
the toner resin particles.
Illustrative examples of optional charge enhancing additives present in
various effective amounts, such as, for example, from about 0.1 to about
20 percent by weight, and preferably from about 1 to about 3 weight
percent include alkyl pyridinium halides, such as cetyl pyridinium
chlorides, reference U.S. Pat. No. 4,298,672, the disclosure of which is
totally incorporated herein by reference, cetyl pyridinium
tetrafluoroborates, quaternary ammonium sulfate, and sulfonate charge
control agents as illustrated in U.S. Pat. No. 4,338,390, the disclosure
of which is totally incorporated herein by reference; stearyl phenethyl
dimethyl ammonnium tosylates, reference U.S. Pat. No. 4,338,390, the
disclosure of which is totally incorporated herein by reference; distearyl
dimethyl ammonium methyl sulfate, reference U.S. Pat. No. 4,560,635, the
disclosure of which is totally incorporated herein by reference; stearyl
dimethyl hydrogen ammonium tosylate; and other known similar charge
enhancing additives providing the objectives of the present invention are
accomplished; and the like.
With further respect to the toner and developer compositions of the present
invention, another optional component present includes the linear
polymeric alcohol comprised of a fully saturated hydrocarbon backbone with
at least about 80 percent of the polymeric chains terminated at one chain
end with a hydroxyl group, which alcohol is represented by the following
formula:
CH.sub.3 (CH.sub.2).sub.n CH.sub.2 OH
wherein n is a number of from about 30 to about 300, and preferably of from
about 30 to about 100, which alcohols are available from Petrolite
Corporation. Particularly preferred polymeric alcohols include those
wherein n represents a number of from about 30 to about 50. Therefore, in
a preferred embodiment of the present invention the polymeric alcohols
selected have a number average molecular weight as determined by gas
chromatography of from about greater than 450 to about 1,400, and
preferably of from about 475 to about 750. In addition, the aforementioned
polymeric alcohols are present in the toner and developer compositions
illustrated herein in various effective amounts, and can be added as
uniformly dispersed internal, or as finely divided uniformly dispersed
external additives. More specifically, the polymeric alcohols are present
in an amount of from about 0.5 percent by weight to about 20 percent by
weight, while as external additives the polymeric alcohols are present in
an amount of from about 0.05 percent by weight to slightly less than about
5 percent by weight.
The stabilizer on the surface of the toner particles can, if desired, be
substantially removed by washing with an aliphatic alcohol containing from
1 to about 25 carbon atoms including, for example, methanol, propanol,
ethanol, butanol, and the like, or water. Separation of washed toner
particles from solution can be achieved by selecting any known classical
separation technique such as filtration, centrifugation and the like.
Classical drying technique such as vacuum drying, freeze drying, spray
drying, fluid bed drying and the like can be selected for drying the toner
.
The following Examples are being submitted to further define various
species of the present invention. These Examples are intended to be
illustrative only and are not intended to limit the scope of the present
invention. Also, parts and percentages are by weight unless otherwise
indicated.
EXAMPLE I
To 90 grams of styrene were added 60 grams of butyl methacrylate and 7
grams of 2,2'azo-bis(2,4-dimethylvaleronitrile), which components were
mixed until dissolved. This mixture was then bulk polymerized by heating
in a one liter glass reactor to 60.degree. C. by means of an oil bath
while the mixture was stirred with a TEFLON.RTM. propeller until 38
percent of the comonomers were converted to polymer, as determined
gravimetry, with a number average molecular weight of 18,000 and a weight
average molecular weight of 31,000 as measured by gel permeation
chromatography. Under these conditions the onset of the gel-effect occurs
at a conversion of 39 percent, therefore the bulk conversion was within 1
percent of the onset conversion. To the resulting comonomer/polymer mix
were then added 6 grams of Pigment Red 48 pigment and 6 grams of cetyl
pyridinium chloride followed by mixing with a Brinkmann PT456G high shear
homogenizer with 10,000 revolutions per minute for 2 minutes to form a
uniform organic phase. The uniform organic phase was then poured together
with 500 milliliters of water containing 0.75 weight percent of
hydroxypropyl cellulose into a two liter stainless steel beaker. The
beaker was placed in an ice bath and using a Brinkmann PT456G polytron
homogenizer the mixture was then vigorously stirred at 10,000 revolutions
per minute for 4 minutes to provide a microsuspension of toner particles
in water. The suspension was then transferred to a 1 liter glass reactor
equipped with a TEFLON.RTM. propeller with a stirring speed of 300
revolutions per minute and the contents of the reactor were heated to
60.degree. C. and controlled at that temperature by means of an oil bath.
After four hours, the suspension polymerization was complete, and the
resulting toner product was poured into two liters of hot, 50.degree. C.,
water. The resulting diluted suspension was then stirred for 15 minutes.
The supernatant liquid comprised of the diluted hydroxypropyl cellulose
was decanted, fresh water was added and the mixture was stirred for 15
minutes to disperse the particles. This washing procedure was repeated
four times with deionized water. After the final wash, the slurry was
poured into a tray and freeze dried to yield clean, dry individual toner
particles of 93 percent of the copolymer of styrene/n-butyl methacrylate,
3.5 percent of the pigment Pigment Red 48 and 3.5 percent of cetyl
pyridinium chloride. Using a Coulter Counter particle sizer, analysis of
the dry toner product was conducted and evidenced an average volume
particle size of 6 microns. As measured by gel permeation chromatography,
the number average molecular weight of the styrene butyl methacrylate
toner resin was 23,000 and the weight average molecular weight was 67,000.
The formed toner product was mixed with 0.3 weight percent of the
colloidal silica (R972) to provide a toner with excellent flow
characteristics, as determined by the very low (less than 3 percent)
fraction of toner retained on a series of vibrating screens of different
mesh sizes. Using a transmission electron microscope, photomicrographs of
the dry toner product were taken and evidenced excellent pigment
dispersion within the particles, that is the pigment particles were
uniformly spread throughout the particles and were not aggregated in the
particle interior or at the surface. Projection efficiency, as calculated
by the ratio of the intensity of specular and diffuse light transmitted
through a fused toner image to the intensity of the total light projected
at the image, was 81 percent. Excellent pigment dispersion is advantageous
as projection efficiency as measured by the fraction of incident light
transmitted through an image is greater when the pigment is more uniformly
dispersed than when the pigment is aggregated within the particle or at
the particle surface. Higher projection efficiency results in superior
color quality. Consequently, less pigment is required and the cost can be
reduced.
Evaluation of the blocking tendency of the above prepared toner was
conducted after permitting 20 grams of the toner to remain in a thermostat
oven set at 55.degree. C. for 24 hours, followed by allowing to cool to
room temperature. No blocking, that is toner agglomeration, was observed
for the above prepared toner.
Print quality evidenced an excellent level of fix as measured by the crease
test method, showing a crease area of less than 65 square micrometers.
EXAMPLE II
The process of Example I was repeated except that the organic phase was
dispersed in water containing 1.0 weight percent of hydroxypropyl
cellulose. The onset of the gel-effect was again 39 percent, and the bulk
conversion was conducted to a conversion of 38 percent. The resulting
toner had an average particle diameter size of 4 microns. other
characteristics of the prepared toner were substantially equivalent to
that of the toner of Example I.
EXAMPLE III
The process of Example I was repeated except that the organic phase was
dispersed in water containing 0.50 weight percent of hydroxypropyl
cellulose. The onset of the gel-effect was again 39 percent, and the bulk
conversion was conducted to a conversion of 38 percent. The resulting
toner had an average particle size diameter of 9 microns. The other
characteristics of the prepared toner were substantially equivalent to the
toner of Example I.
EXAMPLE IV
To 90 grams of styrene were added 60 grams of butyl methacrylate and 7
grams of 2,2' azobis(2,4-dimethylvaleronitrile) which were mixed until
dissolved. This mixture was bulk polymerized by heating in a one liter
glass reactor to 50.degree. C. by means of an oil bath while the mixture
was stirred with a TEFLON.RTM. propeller until 34 weight percent of the
comonomers was converted to polymer (determined gravimetrically) with a
number average molecular weight of 29,000 and a weight average molecular
weight of 55,000 as measured by gel permeation chromatography. The onset
of the gel-effect was determined to occur at a conversion of 33 percent.
Therefore, the difference between the bulk conversion and the onset of the
gel-effect was 1 percent. To the resulting comonomers/polymer mixture were
then added 6 grams of Heliogen Blue pigment, 0.6 gram of divinylbenzene
crosslinking agent and one gram of the linear polymeric alcohol
UNILIN.RTM., available from Petrolite Corporation, with a number average
molecular weight of 600, followed by mixing with a Brinkmann PT456G high
shear homogenizer with 10,000 revolutions per minute for about 3 minutes.
The resulting uniform organic phase was then poured together with 500
milliliters of water containing 0.75 weight percent of hydroxypropyl
cellulose into a two liter stainless steel beaker. The beaker was placed
in an ice bath and using a Brinkmann PT456G polytron homogenizer the
mixture was then vigorously stirred at 10,000 revolutions per minute for 4
minutes to form a microsuspension of toner particles in water. The
resulting suspension of toner was then transferred to a 1 liter Parr
reactor equipped with a magnetic stirrer, an aluminum block heater and
cold water cooling. The suspension polymerization temperature was raised
to 55.degree. C. and held there for 2 hours, then the temperature is
increased to 80.degree. C. in 2 hours and held there for one hour, when it
was then cooled to 25.degree. C., and the toner product was poured into
two liters of hot water. The resulting diluted suspension was stirred for
15 minutes. The supernatant liquid of the diluted hydroxypropyl cellulose
was decanted, fresh water was added and the resulting mixture was stirred
for 15 minutes. This washing procedure was repeated four times. After the
final wash, the slurry was poured into a tray and vacuum dried to yield
clean, dry individual toner particles. Using a Coulter Counter particle
sizer, analysis of the dry toner product was conducted and evidenced an
average particle size diameter of 7.5 microns. As measured by gel
permeation chromatography, the number average molecular weight of the
styrene-n-butyl methacrylate toner resin was 36,000, the weight average
molecular weight was 101,000 and the molecular weight distribution
evidenced two peaks. The toner product was mixed with 0.3 weight percent
of the colloidal silica (R972) to provide a toner with excellent
flowability. Using a transmission electron microscope, photomicrographs of
the dry toner product were taken and evidenced excellent pigment
dispersion within the particles, that is the pigment particles were
uniformly spread throughout the particles and not aggregated in the
particle interior or at the surface. Projection efficiency of the image
formed by this toner was 83 percent.
Evaluation of the blocking tendency of this toner was accomplished by
repeating the procedure of Example I, and the results indicated no
blocking.
Print quality evidenced an excellent level of fix as measured by the crease
test method, showing a crease area of less than 65 square micrometers.
EXAMPLE V
The process of Example IV was repeated except that 500 milliliters of water
containing 1 weight percent of polyvinyl alcohol with molecular weight of
3,000 was used. The onset of the gel-effect was at 33 percent and the bulk
polymerization was conducted to 35 percent. The resulting toner had an
average (volume diameter in all instances) particle size of 3 microns.
This toner was evaluated by repeating the procedure of Example IV and
similar results were obtained.
EXAMPLE VI
The process of Example IV was repeated except that 500 milliliters of water
containing 0.4 weight percent of PLURONIC F87.TM. (BASF) stabilizer was
used. The onset of the gel-effect was at 33 percent and the bulk
polymerization was conducted to 34 percent. The resulting product had an
average volume particle size diameter of 8 microns. This toner was
evaluated by repeating the procedure of Example IV and similar results
were obtained.
COMPARATIVE EXAMPLE
In order to illustrate the effect of varying the bulk conversion on pigment
dispersion and projection efficiency, two additional experiments were
conducted and are described below. For both, the onset of the gel-effect
occurred at a conversion of 39 percent.
The process of Example I was repeated except that the comonomer mixture was
bulk polymerized until 10 percent of the monomer was converted to polymer.
Therefore, the difference between the onset conversion and the bulk
conversion was 29 percent. The resulting toner had an average particle
size diameter of 4 microns. Photomicrographs from a transmission electron
microscope showed the pigment was aggregated at the edge of the particle.
The projection efficiency was 52 percent compared to 81 percent for
Example I.
The process of Example I was repeated except that the comonomer mixture was
bulk polymerized until 30 percent of the monomers was converted to
polymer. Therefore, the difference between the onset conversion and the
bulk conversion was 9 percent. The resulting toner had an average particle
diameter size of 5 microns. Photomicrographs from a transmission electron
microscope showed the pigment was aggregated at the edge of the particle.
The projection efficiency was 65 percent compared to 81 percent for
Example I. A summary of the results for Example I and this comparative
Example is provided in Table 1 and demonstrates that improved pigment
dispersion results with the processes of the present invention when the
initial conversion is closer to the onset of the gel-effect.
TABLE 1
______________________________________
X.sub.b (%)
.increment.X.sub.GE (%)
PE (%) Pigment Dispersion
______________________________________
10 29 52 Poor
30 9 65 Fair
38 1 81 Excellent
______________________________________
X.sub.b represents the percentage of bulk conversion; .DELTA.X.sub.GE
represents the conversion at onset of gel-effect 39 percent minus X.sub.b
; PE represents the projection efficiency; and the Pigment Dispersion is
evaluated by Transmission Electron Microscopy.
Other modifications of the present invention may occur to those skilled in
the art subsequent to a review of the present application. The
aforementioned modifications, including equivalents thereof, are intended
to be included within the scope of the present invention.
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